Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities:
Net loss attributable to NextDecade Corporation	$ (15,238)	$ (4,872)
Adjustment to reconcile net loss to net cash used in operating activities
Depreciation	93	80
Share-based compensation expense (forfeiture)	(2,862)	(1,596)
Loss (gain) on common stock warrant liabilities	6,806	(7,774)
Realized loss on investment securities	0	423
Amortization of right-of-use assets	281	655
Amortization of other non-current assets	708	688
Changes in operating assets and liabilities:
Prepaid expenses	(114)	(17)
Accounts payable	(9)	(384)
Operating lease liabilities	(307)	(502)
Accrued expenses and other liabilities	2,942	(5,483)
Net cash used in operating activities	(7,700)	(18,782)
Investing activities:
Acquisition of property, plant and equipment	(5,481)	(28,163)
Acquisition of other non-current assets	(3,104)	(7,857)
Proceeds from sale of investment securities	0	61,972
Purchase of investment securities	0	(188)
Net cash (used in) provided by investing activities	(8,585)	25,764
Financing activities:
Proceeds from sale of Rio Bravo	0	15,000
Proceeds from sale of Series C Convertible Preferred Stock	34,500	0
Preferred stock dividends	(27)	(28)
Equity issuance costs	(61)	0
Shares repurchased related to share-based compensation	(140)	(111)
Net cash provided by financing activities	34,272	14,861
Net increase in cash and cash equivalents	17,987	21,843
Cash and cash equivalents – beginning of period	22,608	15,736
Cash and cash equivalents – end of period	40,595	37,579
Non-cash investing activities:
Accounts payable for acquisition of property, plant and equipment	18	342
Accrued liabilities for acquisition of property, plant and equipment	975	529
Pipeline assets obtained in exchange for other non-current liabilities	84	0
Non-cash financing activities:
Paid-in-kind dividends on Series A and Series B Convertible Preferred Stock	7,724	6,924
Accretion of deemed dividends on Series A Convertible Preferred Stock	$ 31	$ 97